DE 199 00 264 A1, for example, describes a structural unit of a tie rod for a motor vehicle having a tube provided on at least one side with an inner thread which turns in a first direction of rotation, where an adjustment sleeve that has a corresponding outer thread is screwed into the end of the tube. A shank of a ball joint is screwed into this adjustment sleeve. For this purpose, the shank has an outer thread, which turns in the direction opposite to the first direction that corresponds to the inner thread of the adjustment sleeve. By moving the adjustment sleeve, which has a key surface for attaching a tool for this purpose, the tube and the shank can be moved relative to each other in the axial direction. This means that by rotating the adjustment sleeve, the tube and the shank are moved either towards each other or away from each other. This condition is brought about by the threads that progress in opposing directions. With this adjustment, the structural unit can undergo an axial length adjustment, relative to the common longitudinal central axis of the tube, the adjustment sleeve and the shank, which is of particular significance in the example represented in the document of a tie rod for a motor vehicle for adjusting the wheel alignment of the vehicle. However, the use of an adjustment sleeve between the tube and the shank makes it is necessary to provide two different thread diameters. This causes the force introduced via the key surface to adjust the components relative to each other to be further transferred from the ball joint to the tube via threads of different diameters. Consequently, the smaller diameter thread represents a weak point which could lead to failure with such a tie rod. Beyond this, a further disadvantage with such solutions turns out to be that the shank is inadvertently turned so far out of the adjustment sleeve that receives it that only a small section of thread is available for the transfer of force, or that the shank is even completely removed from the adjustment sleeve. This risk is additionally increased by damaged threads.
In order to prevent unscrewing the shank too far out of the adjustment sleeve, DE 77 32 250 U1 specifies a solution that limits the axial adjustment travel of the tube relative to the shank. The structural unit presented in this document that is built similarly to the previously described tie rod also makes possible the adjustment of the adjustment sleeve via a key surface present for this purpose so that the shank and the tube can be moved relative to each other in the axial direction. However, a special feature of this embodiment is that the threaded connection usually present at the tie rod for fixing the structural unit is used here to fasten a blocking element to the tie rod. The blocking element in the present example is comprised of a metal strip that has a bent end section. This bent end section rests on a planar surface at the shank designed for this purpose. Viewed in the extraction direction of the shank, it further has a groove in which the bent end section of the metal engages when the shank is loosened out of this threaded connection beyond a permissible axial displacement travel. Although the solution described in the document makes possible expedient limiting of the axial travel during adjustment of the structural unit, the manufacturing expenditure for producing the planar surface at the shank is a disadvantage. In addition, this variant embodiment involves a significant assembly expenditure. A further disadvantage is that the metal strip is located outside of the tie rod, and therefore, damage or deformation to the metal strip during the intended use of the tie rod in motor vehicles cannot be excluded so that its function could possibly be negated. In addition, this sheet metal section is subject to increased environmental influences, and therefore there is a risk of it corroding or wearing prematurely.
Furthermore, DE 102 11 066 A1 discloses a structural unit for a tie rod of a motor vehicle having a tube provided with an inner thread in a first direction of rotation, into one end of which an adjustment sleeve is screwed. The adjustment sleeve has an inner thread in the opposite direction of rotation to the first direction of rotation with a shank screwed therein, whose adjustment travel is limited by a blocking element, assigned to the adjustment sleeve, penetrated by the shank.